The invention is based on a goniometer having: a plurality of axes around which a crystal specimen to be examined can be rotated; a radiation source; a detector for Bragg reflections; and a detector for fluorescence radiation.
Such goniometers are known for the structural analysis of crystalline materials. Normally and the lattice constant, the crystal orientation (and for many materials, the texture) are determined. The preferred radiation is the x-radiation of the K.sub.a -lines of copper, molybdenum and other metals. The goniometers used for this purpose are comprised of a radiation source, a specimen table which is pivotable around three axes, with the specimen being secured to the table and, secured on an arm, and a detector with which those parts of the space can be scanned in which reflexes are to be expected.
From the publication "X-ray standing wave technique Application to the study of surfaces and interfaces" by C. Malgrange and D. Ferret in Nuclear Instruments and Methods in Physics Research A 314 (1992), p. 285-296, North-Holland, a method is known by means of which the localization of atoms in crystals and on crystal faces can be determined. This method makes use of the fact that in Bragg reflections standing waves are generated which lead to a strong excitation of fluorescence radiation of the atoms which are attached to or embedded in the lattice.
The variation of the fluorescence intensity as a function of the angle position within the Bragg range makes it possible to determine a space coordinate of the foreign atom. From three linear, independent Bragg reflexes, three space coordinates of the foreign atom can be obtained, and thus a precise localization in the host lattice can be had.
It became evident, however, that it is difficult in practice to determine all three space coordinates of the foreign atoms. This is often due to equipment conditions. The specimen must be rotatable in space around three axes to allow non-coplanar lattice planes to be brought to reflection. The fluorescence radiation occurring during the passage through a Rocking curve often is very weak so that, for the recording of this radiation, the energy-dispersive detector must be brought close to the surface of the specimen.
The possible detectors, i.e., SI(LI) or Ge(Li) semiconductor detectors cooled with liquid N.sub.2, are voluminous and heavy. Because of the spatial overlapping of the individual detectors, these cannot be brought close enough to the specimen.
Further, the equipment used for this method is awkward in its operation and does not utilize the entire available solid angle for the detectors.